Photoconductive zinc oxide sensitized by substituted thiazolidene dyes

ABSTRACT

This application describes electrophotographic material which comprises a photoconductive layer which has been sensitized to light of the blue region of the spectrum by the presence therein of an optical sensitizing dye of the general formula: OR OF THE FORMULA: WHEREIN AT LEAST ONE OF X and Y is an acidic group -(CH2)nCOOM or -(CH2)nSO3M wherein in each group M is a cation and n is an integer from 1 to 4, the other of X and Y when not a said acidic group is a hydrogen atom or an alkyl group containing from one to four carbon atoms or an aryl group.

United States Patent 1191 Hercock et al.

1 1 3,709,685 1 1 Jan. 9, 1973 [54] PHOTOCONDUCTIVE ZINC OXIDESENSITIZED BY SUBSTITUTED THIAZOLIDENE DYES [75] Inventors: Robert JamesHercock; Simon Lindsay Scrutton, both of llford, England [73] Assignee:Iliord Limited, Ilford, Essex, En-

gland [22] Filed: Feb. 18, 1971 [21] Appl. No.: 116,314

[31)] Foreign Application Priority Data 3,125,447 3/1964 Stewart..96/l.7

Primary Examiner- Donald Levy Assistant Examiner-Roland E. Martin, Jr.Att0rney-'Cushman, Darby & Cushman [57] ABSTRACT This applicationdescribes electrophotographic material which comprises a photoconductivelayer which has been sensitized to light of the blue region of thespectrum by the presence therein of an optical sensitizing dye of thegeneral formula:

or of the formula:

O=CNY 1 Ln 128 I S x wherein at least one of X and Y is an acidic group(cH2)nCOOM or (CH2),.SO3M wherein in each group M is a cation and n isan integer from 1 to 4, the other of X and Y when not a said acidicgroup is a hydrogen atom or an alkyl group containing from one to fourcarbon atoms or an aryl group.

4 Claims, 2 Drawing Figures PHOTOCONDUCTIVE ZINC OXIDE SENSITIZED BYSUBSTITUTED THIAZOLIDENE DYES- This invention relates toelectrophotographic material.

Electrophotographic material generally comprises a photoconductive layercoated on a support base which has been rendered at least partiallyelectroconductive. Alternatively it comprises a photoconductive layer onan electroconductive layer which is in its turn coated on a supportbase. One of the most common photoconductive layers comprises zinc oxideparticles in an insulating binder. Specially prepared zinc oxide whichis photoconductive has to be employed and such zinc oxide is usuallyultra violet light sensitive, the sensitivity extending only a shortdistance into the visible light region of the spectrum. Colorelectrophotographic material using zinc oxide photoconductive layers canbe prepared and in this case the surface of the electrophotographicmaterial usually comprises areas which have been selectively sensitizedto the blue, green and red regions of the visible spectrum. There are acomparatively large number of good sensitizing dyes which are capable ofsensitizing zinc oxide to the red and the green regions of the spectrumbut there are only a few dyes which appear to be capable of sensitizingzinc oxide to the blue region of the spectrum.

It is the object of the present invention to provide electrophotographicmaterial, the photoconductive layer of which has been sensitized to theblue region of the spectrum.

According to the present invention there is provided electrophotographicmaterial which comprises a photoconductive layer which has beensensitized to or of the formula ll:

wherein at least one of X and Y is an acidic group (CH ),.COOM or -(CH),,SO -,M wherein in each group M is a cation and n is an integer from 1to 4, the other of X and Y when not a said acidic group is a hydrogenatom or an alkyl group containing from one to four carbon atoms or anaryl group.

M may be a hydrogen atom or an alkali metal such as sodium or potassiumor an alkaline earth such as calcium or ammonium or substitutedammonium.

The whole of the surface of the electrophotographic material may besensitive to blue light by the presence therein of one of the dyes ofthe above formulas or selected regions only of the surface may besensitive. In

the latter case the surface of the photoconductive layer may comprise amosaic of areas each of which has been selectively sensitized to one ofthe regions of the spectrum, blue, green or red;

' The photoconductive layer is preferably photoconductive zinc oxide ina binder but it may be an organic photoconductor, for example polyvinylcarbazole.

The electrophotographic material of the present invention may beprepared by coating a solution of one of the dyes of the above formulasdirectly on to the unsensitized photoconductive layer or particles ofthe photoconductive material, preferably zinc oxide, may have beensensitized by placing them in a solution of the above sensitizing dyesand drying and these sensitized particles may then be coated onto theelectropotographic mater.

Preferably the electrophotographic material of the present invention isprepared by adding a solution of the dye to the coating mixture whichcomprises the photoconductive material, insulating binder, if present,and diluent liquid, before the coating mixture is coated onto thesupport base. When the photoconductive material is zinc oxide thesolution of the dye may be added to the zinc oxide before it is mixedwith an insulating binder, after it has been mixed with the binder butbefore dispersion, or it may be added to the coating mixture containingthe zinc oxide after dispersion.

Therefore according to another feature of the present invention there isprovided a liquid sensitizer for the sensitizing of electrophotographicmaterial which comprises an insulating liquid having suspended thereincharged zinc oxide particles, said zinc oxide particles having been dyedwith one of the dyes of the above formulas l or ll.

Liquid sensitizers for the sensitizing of electrophotographic materialare described in Ser. No. 94,201 filed EXAMPLE The following coatingmixture was prepared:

Fotofax zinc oxide (ex Imperial Smelling Co.) 30 g.

EST-09 resin (ex Cray Valley Products, St.

Mary Cray, Kent, England).

Toluene 4.2g. 20 ml.

This coating mixture was ball-milled for 5 hours and then diluted with15 ml toluene. 0.01 g of the dye 5- l :4 dihydrol-ethyl-4-pyridylidene)-4-oxo-2-thio-3- thiazolidene acetic acid wasdissolved in IQ ml methanol and was added with stirring to the dilutedcoating mixture in a Silverson stirrer. When the dye had been thoroughlydispersed in the coating mixture, the coating mixture was coated on toan electroconductive paper base. A similar photoconductive coating wasprepared and coated on to an electroconductive paper base except thatthe above mentioned pyridylidene dye was not added. A wedge spectrogramof each material was then prepared. These spectrograms are shown in theaccompanying drawing wherein FIG. 1 shows the wedge spectrogram of thedye or blue sensitized zinc oxide material while FIG. 2 shows thespectrogram for the unsensitized zinc oxide material. The unsensitizedelectrophotographic material is light-sensitive in the ulphotoconductivelayer containing zincoxide as the photoconductive substance and whichhas been sensi'tized to light of the blue region of the spectrum by thepresence therein of an optical sensitizing dye of the general formula:

or of the formula:

wherein at least one of X and Y is an acidic group -v '(CH ),.CQ'OM or(CH ),,SO M wherein in each group M is a cation and n is an integer from1 to 4, the other of X and Y when not a said acidic group is a 7hydrogen atom or an alkyl group containing from one to four carbonatoms.

2. Electrophotographic material according to claim 1 wherein thephotoconductive layer comprises zinc I oxidein an insulating binder.

3. Electrophotographic material according to claim 1 which comprises aphotoconductive layer which has been sensitized to light of the blueregion of the spectrum by the presence therein of 5-( l :4dihydro-l-ethyl- 4-pyridylidene) -4-oxo-2-thio-3-thiazolidene aceticacid.

4. Electrophotographic material according to claim 3 wherein thephotoconductive layer comprises zinc oxide in an insulating binder.

2. Electrophotographic material according to claim 1 wherein thephotoconductive layer comprises zinc oxide in an insulating binder. 3.Electrophotographic material according to claim 1 which comprises aphotoconductive layer which has been sensitized to light of the blueregion of the spectrum by the presence therein of 5-(1:4dihydro-1-ethyl-4-pyridylidene) -4-oxo-2-thio-3-thiazolidene aceticacid.
 4. Electrophotographic material according to claim 3 wherein thephotoconductive layer comprises zinc oxide in an insulating binder.